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Research Papers: Flows in Complex Systems

Numerical Simulations and Analysis of a Low Consumption Hybrid Air Extractor

[+] Author and Article Information
Marc Sanchez, Adrien Toutant, Françoise Bataille

PROMES CNRS UPR 8521,
University of Perpignan Via Domitia,
Tecnosud-Rambla de la Thermodynamique,
Perpignan 66100, France

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received October 10, 2016; final manuscript received July 25, 2017; published online September 11, 2017. Assoc. Editor: Wayne Strasser.

J. Fluids Eng 139(12), 121106 (Sep 11, 2017) (10 pages) Paper No: FE-16-1666; doi: 10.1115/1.4037507 History: Received October 10, 2016; Revised July 25, 2017

Hybrid low pressure air extractors are an economic way to enhance indoor air quality. The evaluation of their energetic performances needs the analysis of flow parameters that is typically done with wind tunnel data and numerical simulations. The purpose of this study is to analyze, numerically and experimentally, the flow and the energetic performances of a hybrid rooftop extractor. This innovative extractor has two main features: it works at low difference of pressure, below 50 Pa, and its fan is placed far above the duct outlet, out of the fluid flow. The hybrid extractor works following three modes of operation: stack effect, Venturi effect, and fan rotation. The two first modes of operation allow large energy saving. To analyze the three modes of operation, three sets of corresponding Reynolds-averaged Navier–Stokes (RANS) simulations are developed. The first one allows us to estimate the pressure drop due to the geometry of the air extractor. The second one is used to check the ability of the extractor to generate a suction into the duct in the presence of wind. The final one involves multiple reference frame (MRF) modeling in order to study the flow when the electric motor drives the fan. The numerical simulation configurations are validated with experimental data. A good behavior of the extractor is found for simulations of stack effect mode and Venturi effect mode. The stack effect and the Venturi effect allows the hybrid extractor to work most of the time without electric power. Finally, energetic comparisons are given.

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Figures

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Fig. 1

Schematic view of the studied geometry

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Fig. 2

Numerical domains for pressure drop mode and dynamic mode (cubic domain with bold bounds), static mode (parallelepipedic domain with thin bounds), and boundary conditions

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Fig. 3

Effect of the mesh on the vertical velocity (m s−1) inside the MRF area. The coarse mesh is on the left, the intermediate mesh is at the top, and the fine mesh is on the right. Each cross represents a cell.

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Fig. 4

Mesh for pressure drop mode simulations: (a) cut section in the fan and (b) detail of blades

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Fig. 5

Dimensionless pressure drop as a function of Reynolds number

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Fig. 6

Nondimensionalized velocity field magnitude and nondimensionalized static pressure at Re = 188,462 for pressure drop mode: (a) nondimensionalized velocity (U/Ub) and (b) nondimensionalized pressure ΔPs/(0.5ρUb2)

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Fig. 7

Dimensionless static extraction as a function of Reynolds number

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Fig. 8

Nondimensionalized velocity field magnitude and nondimensionalized static pressure at Re = 22,772 and U = 8 m s−1 for static mode: (a) U/U and (b) ΔPs/(0.5ρU∞2)

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Fig. 9

Dimensionless pressure as a function of Reynolds number

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Fig. 10

Efficiency of the extractor as a function of Reynolds number

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Fig. 11

Relative velocity (m s−1) for dynamic mode, seen from below

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Fig. 12

Streamlines (a), and velocity vectors (b) of the flow below the fan: (a) swirling flow below the fan and (b) flow between the fan and the guard, (z = 1.67 m)

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Fig. 13

Line plot of velocities depending of the radius (a), and position of the different part of the extractor following the radius (b): (a) line plot of the vertical velocity and tangential velocity against the radius at z = 1.67 m and (b) schematic view of the extractor

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